A. Technical Field
The present invention relates generally to electric-powered garden tools. More specifically, the present invention is an electric pole saw featuring a novel saw powerhead mounting bracket assembly comprising interlocking bracket halves molded to conform to the opening and contours of the saw provided between the rear handle, knuckle guard and main body of the saw, to control angular movement or twisting between the bracket-halves and between the powerhead and the bracket.
B. Background
Methods for pruning tree limbs in the past have involved climbing the tree and cutting the limb with a saw while in the tree. This limb removal method presents considerable risk of injury to the person performing the method. Not only does that person have a risk of falling out of the tree, but also the person stands the chance of cutting himself or herself due to the sometimes unstable position the person must assume while in the tree. This risk is further increased with the use of power saws such as electrically-powered or gasoline-powered chain saws because their increased cutting speed makes severe injuries more likely.
To overcome these risks, some persons use “cherry-picker” bucket trucks which include a bucket attached to a crane to prune trees. To use the bucket truck, the saw operator stands inside the bucket, moves the crane to position the bucket adjacent the selected location on the limb, and cuts the limb at the selected location. However, in densely-limbed trees, maneuvering the bucket to the position adjacent the selected location can be difficult and sometimes necessitates cutting additional branches to gain access to the selected location. Thus, this method may require additional time and effort because additional cuts must be made. Further, the additional cuts may be required on limbs which the person does not wish to cut because of the overall desired tree shape. Still further, bucket trucks are expensive to purchase or rent, thereby making this method cost prohibitive for many persons. In addition, because the user may be placed in the vicinity of overhead power lines, this method presents a risk of electrical shock to the user.
To overcome these previously described disadvantages, several prior art devices have been developed which comprise saws mounted on extensions so that the saws may be used to trim the limbs while the user remains on the ground. One prior art saw and extension includes a short pole attached to a typical gasoline-powered chain saw. The pole includes a mechanical control cable extending from the chain saw accelerator to an auxiliary trigger mechanism attached to the pole remote from the chain saw. Thus configured, the user may raise the chain saw to a selected location somewhat remote from the user and accelerate the saw using the auxiliary trigger mechanism to cut the limb at the selected location.
A primary drawback of prior art chain saw extensions having the saw positioned remote from the user is that only relatively short extensions are practical because the weight of the chain saw is centered at a mechanically disadvantageous position. Thus, only limbs which are fairly close to the user may be trimmed using this type of extension because the extension must be relatively short to permit the saw to be lifted and used without undue user strain or fatigue.
Several prior art extension devices have overcome this problem by using lighter weight electrically-powered chain saws. Electrically-powered chain saws are connected to electrical cables which feed electricity to their motors to drive the cutter teeth. By controlling the flow of current through the electrical cables with a variable resistance controller, the speed of the saw may be regulated. Because the electrically-powered chain saws are typically lighter weight than gasoline-powered saws, longer extensions may be used without user strain or fatigue. However, even though chain saw extensions of this type may be longer than gasoline-powered chain saw extensions, they are still limited by the weight of the saw.
Other attempts to overcome the practical weight constraints involve chain saw extensions including a typical gasoline-powered chain saw motor driving a series of belts and pulleys extending through a tubular extension attached to the motor. The belts extend to a sprocket which drives a typical chain saw chain having cutter teeth which travel on a cutter bar mounted to the extension. Thus configured, the saw motor is positioned adjacent the user while the chain is used to cut limbs remote from the user. Because the relatively heavy motor portion of the chain saw is positioned near the user and may even be advantageously positioned behind the user to counter-balance the extension, longer extensions are practical than with the previously described prior art extensions which have the saw motor positioned adjacent the cutter teeth.
There are other prior art chain saw systems which use different power transmission apparatus in place of the belt and pulley system described above. For instance, a prior art chain saw uses a rotating flexible cable to transmit the power from the motor to the cutter bar. Because the cable is relatively light weight, the overall weight of the chain saw extension is reduced to permit longer extensions.
In order to further overcome the weight constraints associated with saws mounted on extensions, at least one prior art device uses the mechanical advantage of a fulcrum and lever to aid in lifting the saw and extension. Thus, longer extensions are practical. However, the fulcrum can make the system difficult to maneuver into position.
There are several electric pole saws on the market that offer the feature of detaching the powerhead from the pole to use as a stand-alone, hand-held chain saw. These electric pole saws use a method for fixing the powerhead to the pole assembly which involves a two-piece bracket to enclose or grip the rear handle area of the powerhead. See FIGS. 1–8, which depict prior art pole saw designs. As shown in FIGS. 2–3 and 4–5, the brackets used in the current technology are stamped metal brackets, with one-half of the bracket containing an engagement finger which engages the trigger/switch mechanism of the powerhead in an activated position. This method uses multiple clamping or fastening points to effect the attachment. As shown in FIG. 8 the prior art brackets use four fastening points to effect the attachment of the powerhead to the pole assembly. The multiple fastening locations between the bracket halves serve to:
1) Provide clamping force between the two halves of the bracket;
2) Directly resist any moment transmitted from the guide bar to the bracket—resulting in relative twisting between the halves of the brackets; and
3) Capture and hold the powerhead trigger/switch mechanism in an activated position to provide electrical continuity between the electric motor and a remote switching mechanism in the pole assembly.
The drawbacks of this technology are:
1) Using stamped brackets to enclose the rear handle area, there are no inherent features in the brackets which resist or control relative motion or twist between the bracket halves; this requires a minimum of two fixing locations to control angular movement between the bracket halves;
2) Four fixing locations are required to control angular movement (the possibility of bi-directional angular movement);
3) Any significant twisting motion between the two bracket halves creates pressure between the powerhead's trigger and the engagement finger on the bracket. This resulting force between the trigger and the bracket's engagement finger can deflect the engagement finger to the yield point—which sometimes results in a malfunction of the pole saw because of the trigger not being actuated by the engagement finger. See FIGS. 9 and 10, which depict the moment from cutting action using a pole saw; and                4) The number of fasteners required to fasten the brackets together complicates the assembly or disassembly of the powerhead to the pole assembly, and lengthens the amount of time required to accomplish assembly or disassembly.        